Creatures 3 kodai:

Hidden song:
Play the "DJ_G.wav" file in the game's sound directory to
hear a hidden rap song from Grendel.

Hints:

Give your Norn something to interact with, such as a ball,
as soon as you can. These guys learn on their own, but the
more you nudge them, the better they become. Also, dump them in the Learning Room when they're little and set the Learning Machine on Auto Teacher.

Be careful when rewarding your Norn. Instead of tickling them, you might slap them by mistake. Wait until they sit still. Also, hitting your Norn more than a few times terrifies it, and if it can speak, it will tell you so. Repeated abuse causes it to die.

To defend Norns from Grendels, try this setup: Take a Sludgegun and connect it to a Creature Detector. Then connect the Detector to a radio set to ten or more (this increases the rate of fire).
Program the Creature Detector to look for Grendels, and place the contraption near the entrance portal. Now, whenever a Grendel approaches, the gun locks onto it and blasts it with gobs of sludge.